1. Field of the Invention
The present invention relates to a low-pressure system and method of producing iron powder and other oxidation forms of iron oxide powder using milled ferric iron oxide powder, or a blend of iron oxides powder. Because of the wide range of iron oxides produced by the instant method, the instant system and method provides the means for producing metallic iron at low pressure in powder form that can be used as an iron supplement for the food industry, or as a way to produce iron in powder form that can be used, for example, for the production of metal parts via powder metallurgy, as well as other applications.
2. Description of the Related Art
Starting from the higher degree of oxidation (hematite) it is possible to produce iron oxides with various degrees of oxidation for a variety of applications, such as magnetite for the production of black pigment or as a toner component. See for example U.S. Patent Pub. No. 20070110648.
A typical high purity hematite would be the iron oxide powder produced in the roasting of steel waste pickle liquor process. The specific surface area of the iron oxide produced by this method is between 500 and 1000 m2/kg.
The properties of iron powder used for the production of components or for the food industry require a small particle size as well as strict requirements concerning residuals. The conventional method for obtaining this quality iron powder is by reduction of hematite in a belt furnace by using a multiplicity of gaseous reduction agents. Usually these processes are run at high temperature of about 1100° C.
The process known today typically consists of crushing and milling the raw material, laying a bed of the milled material in a belt furnace, and reducing the iron oxide to iron with a variety of reducing agents. However, the use of a high temperature sinters the particulates of the reduced iron, forming a cake. Therefore, the next required step is to milling the “cake” in an inert atmosphere to prevent re-oxidation, sieving, classifying and bagging the material. This multi-step approach is described by Clark (U.S. Pat. No. 6,569,220) and Hu (U.S. Pat. No. 7,407,526). Furthermore, both prior art processes use a belt conveyor (fix bed) furnace that require high reducing temperatures and milling after processing because the iron product comes out of the reduction furnace sintered. Before its use the product needs to be milled in an inert atmosphere to prevent re-oxidation of the iron powder. The specific surface area of the product obtained is between 300 and 450 m2/kg. This parameter is important because it defines the reactivity of the product when used as an iron supplement for the food industry.
As known then, in order to produce a high-purity iron powder with desirable characteristics the high temperature and thermodynamics of the process control the rate of the reaction, e.g. the nature of the reactants, the product of the reaction (solids, gases), and the change in the number of mols of the reaction which will produce a change in the rate of the reaction itself. There is a need, then, for a more efficient and flexible method for obtaining iron powder which accounts for pressure as the state variable for defining the system in a way that can be used for the production of specialty products at a lower cost, reducing the use of energy and the process steps required to deliver the final product. These advantages of the instant method results in an environmentally friendly process and, in addition, produce a higher quality product, as follows.